As optical systems continue to increase the volume and speed of information communicated, the need for methods and apparatus operable to facilitate high speed optical signal processing also escalates. Various devices and methodologies have been developed to provide numerous signal processing capabilities on optical signals. Some of these devices attempt to control a diffraction of an input optical signal to facilitate basic signal processing functions.
One such approach uses an optical switching device having a plurality of adjacent reflective strips disposed above a conductive inner surface. In one state of operation, the adjacent reflective strips remain in a single plane and substantially reflect optical signals received. In another mode of operation, alternate adjacent strips are pulled down parallel to the inner surface to create a bi-planar diffraction grating. The resulting two parallel planes of reflective strips create diffraction of the input optical signal in numerous directions. Diffracted portions of the input signal can be detected and used as a modified output signal.
This approach suffers from a number of deficiencies. For example, where a normal incident input signal is used, the power of the output signal is split equally between the two first order beams, which are diffracted in different directions. This results in difficulties maintaining two substantially equal outputs, because only a small portion of the diffracted signal can be recovered using a single detector or a single fiber. Recovering additional portions of the diffracted signal typically requires collecting diffracted portions traveling in numerous directions and recombining them. This approach typically results in additional system components, complexity and cost.
Another approach to diffraction based signal processing involves orienting a solid membrane diffraction grating at an angle to the incoming optical signal to cause a majority of the diffracted output signal to travel in one direction. Early variable blazed grating apparatus attempted to implement deformable membranes that could be selectively deformed to cause diffraction substantially in one direction. Supporting the membranes in these devices required use of an elastomeric substance under the entire membrane, which contacted the entire membrane. The combination of a large area membrane and a confining supporting material generally resulted in slow device operation and large required drive voltages.
Recently, variable blazed gratings have been used in spectral analyzers to improve the frequency sensitivity of those devices by directing high powered optical beams in specific directions. These devices use a series of adjacent slats (typically ranging from 50,000 nanometers to 80,000 nanometers in width) that are capable of rotating by a very small amount to direct low order diffraction modes in a specific direction. The high power of the incident beams in this application generally requires that the slats be constructed as wide as possible. The large width of the slats severely limits the blaze angle (less than two degrees) that can be obtained using this approach. In addition, the width of the slats significantly limits the frequency at which these devices can change states, and increases the drive voltage necessary to rotate the slats.